1. Field of the Invention
This invention concerns a culture which can bring about fermentation and natural leavening in breads and related baked goods. In particular, this invention relates to whole grain barms embodying this culture; the culture itself which contains a bacterial and a yeast species; the components of the culture as isolates; a method for initiation and reproducibly producing the barms and the culture that they contain; and methods for the use of the barms, the culture and the isolates.
2. Prior Art
The term "barm" is often used to refer to a brewing liquid containing a yeast. The term has also been used to refer to a "starter" for naturally leavened baked goods. Natural leavening and its use in baking and other food preparation processes are ancient concepts which predate the baker's yeast and/or baking powder leavening commonly in use today. Natural leavening is now understood to rely upon the action of various native organisms in flour and other foods such as milk to generate a leavening gas by fermentation mechanisms.
Natural leavening has numerous advantages. For one, goods prepared with natural leavening often have a superior taste and excellent aroma. For another, leavening is carried out without adding chemical agents so that completely natural and hygienic baked goods result. Natural leavening is compatible with most common flours--including whole grain flours--so that an especially nutritious product is possible. Natural leavening processes generally generate acidic materials such as lactic and acetic acids in the baked product. This acidity prevents spoilage of the product and thus enhances its storage life without resort to added chemical preservatives.
Notwithstanding these advantages, the natural leavening process has fallen into disfavor. Its principal present application in the United States is in the leavening of "San Francisco sourdough" French bread products. One problem presented by classic natural leavening has been a lack of reproducibility, with different grains and flours giving different results from day to day. Another problem that has interfered with the broad use of the process has been a lack of stability such that the starter often must be refreshed or rebuilt several times a day. A third problem is a lack of consistent activity. The "starters" often die or become inactive with time.
These three problems are reflected in the common practices of commercial sourdough bakers of having a preferred "secret" starter sponge or barm which has been "used for generations" and often of rebuilding or renewing this sponge two or three times daily.
References to natural leavening processes and materials include Bakers Digest, (1970) Vol 44, No. 2, pp 48-50 in which Kline, Sugihara and McCready describe the nature and history of the San Francisco sourdough bread leavening and baking process. In this article they describe the practice of continual renewal and describe the use of conventional white bread flours in the process. In a second article appearing at Bakers Digest, (1970) Vol 44, No. 2, pp 51-53, 56-67 Sugihara, Kline and McCready describe the microbiological aspects of the same process. They show that the classic starter sponges contain a yeast Saccharomyces exiguus or its nonspore-forming equivalent Torulopsis holmii and, occasionally, Saccharomyces inusitatus, which is now regarded as a strain of baker's yeast, Saccharomyces cerevisiae. They also reported that bacteria are present in starter sponges as well. This reference compares these bacteria with those found in rye bread starters. Tentatively, the bacteria is described as a Lactobacillus. In Applied Microbiology (March 1971) Vol 21, No. 1, p 456-458, Sugihara et al give further preliminary classification information about the bacteria. In Applied Microbiology (June 1972) Vol 23, No. 6, pp 1153-1159 Ng reports studies which further classify the bacteria as a heterofermentative Lactobacillus. Ng also reports in Applied and Environmental Microbiology, Vol 31, No. 3, March 1976, pp 395-398 that the bacteria has been further characterized and named Lactobacillus sanfrancisco.
Patent references include U.S. Pat. No. 558,393 of Kellogg which shows a process for production of a cooked grain product which is treated at temperatures between 110.degree. F. and 140.degree. F. or between 40.degree. F. and 60.degree. F. to prevent fermentation; U.S. Pat. No. 1,041,629 of Jaquet which discloses that grain, when wet under certain conditions, will ferment spontaneously; U.S. Pat. No. 1,910,967 of Ruckdeschel which describes a two step method for making rye bread in which an acid fermentation is favored in a first step and a yeast rise is favored in the second; U.S. Pat. No. 2,322,940 of Kirby et al which shows several species of Lactobacillus as acid-forming components of bread souring materials; U.S. Pat. No. 2,476,242 which describes a process for preparing a white rye flour and yeast-based sour flour which is storable; U.S. Pat. No. 2,857,280 of Williams et al which describes a frozen pancake batter which contains a Lactobacillus aand/or a nonpathogenic bacterial species of the Lactic group of the genus Streptococcus and a Saccharomyces or Torulopsis yeast; two U.S. Pat. Nos. 3,891,773 and 3,734,743 of Kline et al, which essentially cover the material of their above-described papers on the microorganisms in sourdough french bread; U.S. Pat. No. 3,963,835 which describes the use of Lactobacillus plantarum in baking products; and U.S. Pat. No. 4,021,581 of Sing which discloses a process for rapidly and economically growing Lactobacillus sanfrancisco.